An injection molding unit of this type is known from DE 198 31 482 C1, wherein a plane of separation is provided therein between an injection motor and a dosing motor, said plane serving to separate the spheres of influence of the two electromechanical drives from each other. An electric motor incorporating a rotor and a stator can be used as the dosing motor. The injection motor which is located behind the dosing motor as seen from the plasticizing unit is formed by a spindle drive means which is mounted on a supporting element. The injection bridge carrying the two motors is guided on spars which form a framework of forces via the supporting element for the spindle drive means at the rear.
WO 2008/052959 A1 discloses a compactly built drive device for an injection molding machine comprising an electromechanical injection motor and an electromechanical dosing motor. The two hollow-shafted motors act on a shaft that is common to the motors. Consequently, for the purposes of the injection molding process, this drive device together with the driven dosing motor must form a counter hold means for the injection motor. In consequence, the dosing motor not only has to be dimensioned to support a larger torque than is actually necessary, but the total energy consumption of the system also rises.
From EP 0 576 925 A1, there is known an injection molding unit wherein two liquid-cooled servo motors for driving the nozzles i.e. for placing the injection molding unit on a mould carrier and for the injection process are arranged one behind the other with their effective axes aligned with one another. The dosing motor, with which the rotation of the conveying means i.e. the feed screw is effected, is mounted on a separate supporting element.
DE 10 2006 007 438 B3 discloses a drive means for an injection molding unit which comprises just one hollow shafted motor and, where necessary, an auxiliary drive means for the metering and injection processes. Mounted within the hollow shafted motor are two shafts which can also convert axial movements by means of a spline-shaft coupling. The dosing and injection processes are effected serially in alternating manner using one and the same hollow shafted motor. In order to separate the movements from one another, the zones of influence of the two parts of the motor are separated from each other by an axial bearing in the driven shaft. In addition, a free-wheel device is provided in the front part of the hollow shafted motor for the movement required purely for dosing purposes and it can be operated in conjunction with a braking means when the injection process is being effected by the rear part of the hollow shafted motor.
DE 10 2007 027 212 A1 proposes a drive device for an injection molding unit wherein a drive spindle for the dosing and injection processes has a threaded section which is in engagement with a driven spindle nut. A further spindle, which is rotatable by an associated drive motor, cooperates with the drive spindle. The two spindles are coupled to one another by a threaded connection for operational purposes.